When a magnetic medium in a hard magnetic disk (hereinafter will be simply called as a magnetic disk or disk) used for a computer system is abnormal, since an error is caused in write data or read data, predetermined test data, for example, data of FFh are written on a predetermined track of the disk and then the written data are read by a certifier and whether good or bad of the magnetic medium is certified (an evaluation by an electric characteristic inspection). Incidentally, “h” in the FFh indicates hexadecimal notation and FF implies data of which all bits are “1”.
Bit errors to be detected by the certifier include such as a missing of bits, so called missing error (including a bit of which level drops below a predetermined threshold value), a spike error due to bit spiking, a positive modulation error and a negative modulation error. Further, other than the above errors, an error detected when performing detection whether a bit is read under a condition where data are erased is identified as an extra error.
In a hard disk drive device (HDD), a coil type magnetic head (an inductive head) is used for data writing and an MR head is used for reading. These writing head and reading head are integrated as a combined head and a disk recording density is increasing day by day.
For the above referred to defect inspection, there are what is called as concentric inspection in which a magnetic head is caused to seek respective tracks of a magnetic disk and to scan the disk in a concentric shape along the respective tracks to detect defects and what is called as spiral inspection in which the magnetic head (a head carriage) scans the disk in a spiral shape to detect defects.
The former concentric inspection usually takes time for inspecting the entire surface of a disk and shows a poor efficiency. Moreover, recently the number of tracks for inspection is increased and the quality of disks is improved. Actually, the number of tracks having defects is at most about 100 through 200 with respect to the entire tracks. For this reason, a thinning concentric inspection in which a part of tracks to be inspected is thinned out and the latter spiral inspection are frequently performed. Further, even in the latter spiral inspection, the spiral inspection with a thinned pitch is sometimes performed.
As prior art of this sort of defect inspection devices, technology disclosed in JP-H10-275434A, JP-2000-57501A and JP-2000-57502A is to be mentioned.
Depending on a high recording density demand, an actual size of a head assembly (a magnetic head+a suspension spring) used in a recent HDD is about 15 mm˜20 mm long for a disk less than 1.8 inch and the size of a magnetic head which is provided at the top end of the suspension spring is about 0.5 mm×0.5 mm or less and is very small even when including a slider of about 3 mm×3 mm. Moreover, the gap between the magnetic head and the magnetic disk comes close to a distance from ten and several nm to several tens nm.
For this reason, when there is a circle scratch, the magnetic disk is highly possible to be determined as defective. Conventionally, such circle scratch was detected by an optical defect inspection, however, some of magnetic disks having a high recording density of these days which are determined acceptable by the optical inspection are determined defective because of detection of a circle scratch by an electric characteristic inspection. For this reason, the judgment of defective disks with the optical inspection is performed by enhancing the detection accuracy of such circle scratch, however, with such measure, disks having a defect other than the objective circle scratch are possibly determined defective which causes a problem to worsen a yield for disk production.
For this reason, detection of such circle scratch by an electric characteristic inspection is demanded, however, at the present time, since the detection limited only to the circle scratch is difficult, detection of line shaped defects is actually performed. Since the line shaped defects include a variety of defects, when the detection of line shaped defects is performed, many defects other than circle scratches are detected, which causes a problem.
Since usual line shaped defects are not ones of circumferential shape, the line shaped defects do not affect much to the electrical characteristics of the disks. Therefore, even if such line shaped defects exist, the disks do not frequently determined defective with regard to the electrical characteristics. When circle scratches are required to be extracted among curved line defects such as S shaped defects and many line shaped defects, criteria such as curvature and curving direction thereof have to be included for the judgment, which makes the judgment difficult and requires time for the judgment.